This application is related to Japanese applications No. 2001-017201 filed on Jan. 25, 2001 whose priority is claimed under 35 USC xc2xa7 119, the disclosures of which are incorporated by reference in their entirety.
1. Field of the Invention
The present invention relates to a laser processing device, and more particularly to a laser processing device in case where a transfer method is used as a method for forming an organic substance layer in an organic electroluminescent display panel using an organic electroluminescent element at its pixel luminescing portion having an element structure of a substrate; a first electrode; an organic substance layer including at least a luminous layer; and a second electrode.
The present invention also relates to an organic electroluminescent display panel using the laser processing device.
2. Description of the Prior Arts
A demand has rapidly been increasing to a display panel as a man-to-machine interface as the times of multi-media has come around. A liquid crystal display panel has widely been used, among various display panels, because of the characteristics of thin-size, reduced consumptive electric power, or the like.
Pixel portions of R (red), G (green) and B (blue) are required to be formed for establishing a full-color display on the liquid crystal display. The liquid crystal display achieves this object by using a color filter transmitting each color of R, G and B. A well-known popular photolithography method has generally been applied for minutely patterning these color filters into R, G and B.
However, the patterning has been difficult nowadays due to a progressed high precision of the display. Further, the influence given to the environment is concerned, since developing solution such as organic solvent is used in a great amount upon developing.
In recent years, a transfer method has been paid an attention as a pattern forming method of a color filter made of an organic substance.
When the transfer method is applied for a method for forming the color filter of the liquid crystal display device, a thin-film layer that is to be transferred is firstly formed onto a donor substrate comprised of a PET (polyethylene terephthalate) film or the like by a vapor-deposition method, spin coating method or printing method. The resultant thin-film layer is then adhered to an acceptor substrate on which the film is expected to be formed. A laser beam from a laser beam source is applied from the donor substrate to thereby transfer the thin-film layer formed at the side of the donor substrate to the acceptor substrate side. Thereafter, the donor substrate is detached, whereby the portion to which the laser beam is irradiated is transferred to the acceptor substrate.
The structure of the donor substrate used for the transfer method is not specifically limited. When laser beam is utilized for an energy source, the use of a film having a thermal transmission layer, light-to-heat conversion layer or separate layer formed thereon enhances a transfer efficiency.
The excellent points of the transfer method are that the patterning is not specifically required for forming the thin-film onto the donor substrate and that the portion irradiated by laser beam is only transferred onto the acceptor substrate from the donor substrate. Further, a small adverse affect to the environment can be taken as one of the excellent points of the transfer method.
Frequently, the donor substrate and the acceptor substrate are fixedly adhered with each other upon performing the transfer process. The film-formation principle lies in the fusing or sublimation of the area irradiated by laser beam or heat because of an instantaneous rise in the temperature of this area. This is an instantaneous phenomenon. Therefore, the organic substance thin-film remains intact, whereby the film formed on the donor substrate is exactly formed onto the acceptor substrate side.
FIG. 5 is a schematic view showing a process for forming an organic substance thin-film such as a color filter on a acceptor substrate with the transfer method.
A donor substrate (101) has an organic substance thin-film layer (102) formed by a known method such as the spin coating method or vapor-deposition method. The donor substrate (101) may be a single PET film, but in many cases, it has a light-to-heat conversion layer, thermal transmitting layer or separate layer suitably formed thereon for performing a satisfactory transfer.
The donor substrate (101) adheres to an acceptor substrate (103) on which, for example, a transparent electrode line is wired such that the side of the donor substrate (101) having the organic substance thin-film layer (102) formed thereon contacts with the acceptor substrate (103). A roller method or vacuum laminate method is frequently used for adhering the donor substrate to the acceptor substrate.
Subsequently, laser beam (105) is irradiated from the side of the donor substrate (101) by a laser beam source (heat source) (104). The excessive large distance between the heat source (104) and the donor substrate (101) reduces a laser intensity, thus inconvenient. On the other hand, satisfactory transferring conditions can be set by suitably mounting a lens (106) or slit plate (107) between the heat source (104) and the donor substrate (101).
On the other hand, an organic electroluminescent display panel using an organic electroluminescent element at its pixel luminescing portion has been developing as a display panel in the future generation that takes place of the liquid crystal display panel.
The organic electroluminescent display panel using an organic electroluminescent element at its pixel luminescing portion has an element structure of a substrate; a first electrode; an organic substance layer including at least a luminous layer; and a second electrode. It has features of a thin-size, completely solid-state, plane self-luminescence and high-speed response.
FIG. 6 is a structural sectional view of an organic electroluminescent element having a general structure wherein luminescence is taken out from the first electrode side.
A transparent first electrode (202) is formed on a transparent substrate (201). An organic substance layer (203) including at least a luminous layer and a second electrode (204) made of a metal thin film are successively formed on the first electrode (202).
Luminescence (205) is obtained via the transparent substrate (201) and the transparent first electrode (202). ITO (indium tin oxide) is used as the first electrode (202)in most cases. The ITO is widely utilized in a liquid crystal display panel. The formation of the wiring is easy by using the ITO, whereby its technique can also be applied to the organic electroluminescent element.
The principle of the luminescence in the organic electroluminescent element is based upon the fact that the application of voltage between the electrodes injects an electron from one electrode to the luminous layer while injects a hole from the other electrode to the same layer, which brings a plane luminescence from the luminous layer because of the re-combination of these electron and hole.
Therefore, either one of the electrodes is desirably transparent in order to obtain the plane luminescence. In most cases, a transparent conductive film is used as the first electrode formed on the substrate for taking out the luminescence. In this case, the substrate has to be transparent for taking out the luminescence. Specifically, the element structure becomes as follows: a transparent substrate; a transparent first electrode; an organic substance layer including at least a luminous layer; and a second electrode that does not have to be transparent.
Subsequently, a manufacturing process of the organic electroluminescent element will be explained. The first electrode formed on the substrate is made generally of the ITO as described above. Specifically, the first electrode is formed by forming the ITO on the whole surface of the substrate by a sputtering method, followed by performing a patterning by a known photolithography to a predetermined shape. The processing precision of the ITO is high even though the process requires a high-precise technique, thus no problem.
Further, a metal thin film is used as the second electrode formed on the organic substance layer. The second electrode is formed by an electron beam method, sputtering method or vapor-deposition method.
As for the formation of the organic substance layer including at least the luminous layer, the organic substance layer is generally formed by the vapor-deposition method in case where the layer is made of a low-molecular material, while it is generally formed by the spin coating method in case where the layer is made of a high-molecular material.
However, the luminous layer is required to have different colors each corresponding to R, G and B upon manufacturing a display panel using the organic electroluminescent element at its pixel luminescing portion. This can be done by using a shadow mask method, ink jet printing method or the like. However, it is extremely difficult to execute the process with high precision by these methods.
In order to solve the problem concerning the high-precision, a transfer method used for forming a color filter of the liquid crystal display panel has been proposed to be applied to a method for forming a thin-film layer of the organic electroluminescent element as a new film-forming method for the organic electroluminescent element.
Forming the organic substance layer including at least the luminous layer in the organic electroluminescent element by the transfer method is disclosed in, for example, Japanese Unexamined Patent Application Nos. HEI9-167684, HEI10-208881 and HEI11-260549. Specifically, the disclosed method is as follows. Firstly, the organic substance thin-film layer to be transferred is formed on a donor substrate made of a PET (polyethylene terephthalate) film by the vapor-deposition method, spin coating method or sputtering method. The resultant is adhered to an acceptor substrate on which the film is expected to be formed. Thereafter, energy such as laser beam or heat is applied to the resultant from the donor substrate side to, thereby transfer the organic substance thin-film layer formed on the donor substrate onto the acceptor substrate. The organic substance used for the organic electroluminescent element may be a low-molecular or high-molecular material.
Various methods such as the vapor-deposition method, ink jet method, spin coating method, printing method or the like have been applied so far for forming the organic substance layer.
The advantage of the transfer method is that the high-precision which is difficult to be obtained in the shadow mask method or ink jet method can easily be achieved. This is because the laminated thin-film formed on the donor substrate is formed such that only the portions of the thin-film irradiated by the laser beam or heat source upon the transfer are exactly transferred in the reverse order on the acceptor substrate. Another advantage is that the patterning is not specifically required upon forming the organic substance layer on the donor substrate.
Next, the method for forming each layer will be explained. The first electrode is formed by using the ITO with a known photolithography. As for the organic substance layer, it is generally formed by the vapor-deposition method if made of a low-molecular material while it is formed by the spin coating method if made of a high-molecular material. The luminous layer is required to have different colored portions upon manufacturing the display panel having the organic electroluminescent element used in the pixel luminescing portion. This can be achieved by using donor substrates each having a differently colored luminous layer for performing the successive transfer. A metal thin-film is used for the second electrode formed on the organic substance layer. The second electrode is formed by the electron beam method, sputtering method or vapor-deposition method.
The organic substance layer used for the pixel luminescing layer in the organic electroluminescent display panel has been known as having a remarkably low resistance. When left in the atmosphere, in particular, it is damaged by water content or oxygen content, entailing a problem that it is difficult to manufacture a good-looking display panel.
In most cases, a sealing process is performed under the present conditions so as not to expose the first electrode, the organic substance layer including at least the luminous layer and the second electrode to the atmosphere. To be absolutely sure, absorption agent or oxygen absorbent is sometimes sealed.
This is greatly different from the color filter of the liquid crystal display panel. Specifically, the color filter of the liquid crystal display panel has little limitation on its thickness that is several microns in most cases. Therefore, strict limitation is not established on the distribution and unevenness of the thickness.
Further, transmitting a specific wavelength in backlight or reflected light is good enough for the color filter. Therefore, the color filter may be formed in most cases by using a color film in which pigment or the like is dispersed. Accordingly, it has sufficient resistance in the atmosphere, so that the environmental conditions upon the transfer are not specifically considered. As shown in FIG. 5, the transfer can be executed in the atmosphere.
When the organic substance layer used for the pixel luminescing portion of the organic electroluminescent display panel is formed by the transfer method, the damage is severe when the organic substance layer is exposed in the atmosphere, since it has a thickness of 2000 angstroms at most that is remarkably thinner than the color filter.
Different from the color filter of the liquid crystal display panel that transmits light, the organic substance layer used for the pixel luminescing portion of the organic electroluminescent display panel is charged with electricity. Therefore, the organic substance layer is very delicate to the distribution and unevenness of the thickness. The organic substance layer has a structure such that a plurality of organic thin films are laminated for enhancing its performance. Therefore, the execution of the transfer process in the atmosphere entails a problem of causing a separation at the boundary of each thin film.
Considering the above-mentioned points, the transfer process should be performed under the environmental condition with the influence from water content or oxygen content eliminated compared to the formation of the color filter in the liquid crystal display panel, in case where the organic substance layer used for the pixel luminescing portion of the organic electroluminescent display panel is formed by the transfer method.
However, sufficient research has not been made so far for forming by the transfer method the organic substance layer used for the pixel luminescing portion of the organic electroluminescent display panel. It has not been considered that the organic substance layer including at least the luminous layer should be protected from the surrounding environmental condition.
The present invention is accomplished in view of these circumstances, and aims to provide a laser processing device and an organic electroluminescent display panel using the same, which is capable of protecting an organic substance layer including at least a luminous layer from the surrounding environmental condition, when the organic substance layer used for a pixel luminescing portion of the organic electroluminescent display panel is formed by a transfer method.
According to one aspect of the present invention, the invention provides a laser processing device comprising: an optical system having a laser beam source, and an air-tight chamber provided separately from the optical system, wherein the chamber has a transparent portion for transmitting a laser beam emitted from the laser beam source, on a light-receptive face thereof receiving the laser beam, the chamber is capable of accommodating a donor substrate on which an organic substance layer to be transferred is formed and an acceptor substrate onto which the organic substance layer is transferred from the donor substrate by the laser beam transmitted through the transparent portion, and the inside of the air-tight chamber is in an inert gas atmosphere or in a vacuum atmosphere.
According to the laser processing device having the above-mentioned structure, the organic substance layer can be protected from the surrounding environmental condition upon forming the organic substance layer used for the pixel luminescing portion of the organic electroluminescent display panel. This is because the inside of the air-tight chamber is in the inert gas atmosphere or in the vacuum atmosphere.
According to another aspect of the present invention, it provides an organic electroluminescent display panel manufactured by using the laser processing device, this display panel having a following element structure of a substrate; a first electrode; an organic substance layer including at least a luminous layer; and a second electrode wherein said organic substance layer including at least the luminous layer is formed by a transfer method.
The organic electroluminescent display panel having the above-mentioned structure can yield satisfactory luminescence, in spite of having the same element structure as the conventional panel. This is because the organic substance layer including at least the luminous layer is protected from the surrounding environmental condition as described above upon its formation.